Fast digital carrier frequency error estimation algorithm using synchronization sequence

a digital carrier and error estimation technology, applied in the field of communication systems, can solve the problems of increasing the appearance of a bias error in the carrier frequency error estimation, too expensive computationally for certain applications, and undesirable methods,

Active Publication Date: 2007-02-01
HARRIS GLOBAL COMMUNICATIONS INC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Digital carrier frequency error estimation using the DFT approach described above may be too costly computationally for certain applications even if a fast Fourier transform (FFT) is used.
Similarly, the PLL approach entails additional hardware and processing complexity that make this method undesirable compared to simpler algorithms.
A limitation of the HCDR approach is the appearance of a bias error in the carrier frequency error estimate that increases with the degree of the offset and is independent of the symbol energy to noise energy (Es / No) level.
The addition of a compensation factor may reduce the mean estimation error, however, this results in increased complexity along with an increase in the variance of the estimation error.

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  • Fast digital carrier frequency error estimation algorithm using synchronization sequence
  • Fast digital carrier frequency error estimation algorithm using synchronization sequence
  • Fast digital carrier frequency error estimation algorithm using synchronization sequence

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Embodiment Construction

[0024] In accordance with one aspect of the invention, an improved digital frequency estimation algorithm is provided that overcomes the complexity of DFT algorithms and the additional overhead associated with PLL approaches by “back processing” the synchronization section of a received waveform. The algorithm allows for a frequency estimate to be formed from a relatively short segment of input data using overlapping symbols extracted from the data. By correlating over short segments, the signal-to-noise ratio is improved for the estimate. Since a synchronization (SYNC) sequence is known by a demodulator in a receiver, the demodulator can store the received digitized inphase (I) and quadrature (Q) baseband signals during the SYNC section of the waveform. Once SYNC is detected, the stored I and Q signals received during the SYNC section are read out of memory and processed to determine the carrier frequency error. The carrier frequency error can be determined entirely in the time-dom...

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Abstract

Methods and apparatus for determining carrier frequency error of a serial offset quadrature pulse shaped signal, such as a minimum shift keyed (MSK) signal, are disclosed. Carrier frequency error is determined by receiving a quadrature pulse shaped signal having a synchronization sequence, detecting synchronization of the quadrature pulse shaped signal, and storing a baseband inphase (I) signal and a baseband quadrature (Q) signal of the synchronization sequence while detecting synchronization. After detecting synchronization, segments of the stored baseband I and Q signals are read and correlated with a spreading sequence. Carrier frequency error is then estimated based on phase differences between each of the correlated segments.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority of U.S. Provisional Patent Application Ser. No. 60 / 703,180, filed Jul. 28, 2005.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH [0002] This invention was made with Government Support Under Agreement No. DAAB07-03-9-K601 awarded by the United States Army. The Government has certain rights in the invention.TECHNICAL FIELD [0003] The present invention relates, in general, to communication systems. More specifically, it relates to enhanced methods and apparatus for determining carrier frequency error in a receiver. BACKGROUND OF THE INVENTION [0004] Carrier frequency error estimation is often performed in a receiver of a communication system to eliminate offsets between a received signal's actual frequency and a frequency assumed by the receiver. An optimal maximum likelihood estimator (MLE) for the offset is given by the location of the peak of a spectral plot for the signal. Used with a discrete Fourier t...

Claims

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Application Information

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IPC IPC(8): H04L27/06H04L7/06
CPCH04B1/70752H04L27/0014H04L2027/0067H04L2027/0048H04L2027/003
InventorRASMUSSEN, DONALD JOHNBARNETT, GREGORY THOMAS
OwnerHARRIS GLOBAL COMMUNICATIONS INC